Laser ashing of polyimide for semiconductor manufacturing

ABSTRACT

A system for laser ashing of polyimide for a semiconductor manufacturing process is provided. The system includes: a semiconductor chip, a top chip attached to the semiconductor chip by a connection layer, a supporting material, a polyimide glue layer disposed between the supporting material and semiconductor chip, a plasma asher, and an ashing laser configured to ash the polyimide glue on the semiconductor chip.

CROSS REFERENCE

This application is a divisional of U.S. patent application Ser. No.13/285,408, filed on Oct. 31, 2011, which is currently pending, andwhich is incorporated by reference in its entirety.

BACKGROUND

This disclosure relates generally to the field of semiconductor chipmanufacturing, and more particularly to removal of polyimide glue from asemiconductor chip during manufacturing.

During semiconductor manufacturing, multiple semiconductor chips may beformed in a single piece of a substrate (for example, a siliconsubstrate). The semiconductor chips may include various structures, madefrom various materials such as silicon oxide, silicon nitride, or metal.The semiconductor chips need to be separated in the later stages of thesemiconductor manufacturing process. For example, this separation may beachieved by dicing the substrate containing the semiconductor chips. Thesubstrate containing the semiconductor chips may require attachment to arigid supporting material during dicing, so as to avoid damage to thesemiconductor chips during dicing. A glue, which may be a polyimideglue, may be used to attach the supporting material to the substrate.After dicing, the supporting material and the glue need to be removedfrom the diced semiconductor chips.

Some polyimide removal methods, which may be applied to polyimide glueon a semiconductor chip, include wet etching and plasma ashing. Thesemethods may be isotropic, which may cause damage to structures locatedon the semiconductor chip underneath the polyimide, and relatively slow,limiting throughput for the semiconductor manufacturing process. Wetetching may be performed using N-methyl pyrrolidinone (NMP); however,the etch rate of wet etching with NMP is relatively slow. Plasma ashingmay be performed using oxygen (O₂) plasma or hydrofluoric plasma. Forplasma ashing in O₂, the etch rate is also relatively slow; it may takemore than 5 hours to remove the polyimide. The required temperature forO₂ plasma etching is also relatively high (up to 250° C.), which maydamage the semiconductor chip. For hydrofluoric plasma ashing, the etchrate may be higher, but other materials in the semiconductor chip, suchas silicon oxide, silicon nitride, or metal may also be etched alongwith the polyimide, damaging the semiconductor chip.

SUMMARY

In one aspect, a method for laser ashing of polyimide for asemiconductor manufacturing process using a structure, the structurecomprising a supporting material attached to a semiconductor chip by apolyimide glue, includes releasing the supporting material from thepolyimide glue, such that the polyimide glue remains on thesemiconductor chip; and ashing the polyimide glue on the semiconductorchip using an ablating laser.

In another aspect, a system for laser ashing of polyimide for asemiconductor manufacturing process includes a semiconductor chip; apolyimide glue located on the semiconductor chip; and an ablating laserconfigured to ash the polyimide glue on the semiconductor chip.

Additional features are realized through the techniques of the presentexemplary embodiment. Other embodiments are described in detail hereinand are considered a part of what is claimed. For a better understandingof the features of the exemplary embodiment, refer to the descriptionand to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 illustrates a flow chart of an embodiment of a method for laserashing of polyimide.

FIG. 2 is a schematic block diagram illustrating an embodiment of asemiconductor chip attached to a supporting material by a polyimide gluelayer.

FIG. 3 is a schematic block diagram illustrating an embodiment of thesemiconductor chip of FIG. 2 during release of the supporting member.

FIG. 4 is a schematic block diagram illustrating an embodiment of thesemiconductor chip of FIG. 3 after release of the supporting member.

FIG. 5 is a schematic block diagram illustrating an embodiment of thesemiconductor chip of FIG. 2 during laser ashing of the polyimide gluelayer.

FIG. 6 is a schematic block diagram illustrating an embodiment of thesemiconductor chip of FIG. 5 after laser ashing of the polyimide gluelayer.

FIG. 7 is a schematic block diagram illustrating an embodiment of thesemiconductor chip of FIG. 6 after attachment of a top chip.

DETAILED DESCRIPTION

Embodiments of systems and methods for laser ashing of polyimide areprovided, with exemplary embodiments being discussed below in detail.Laser ashing of polyimide may be relatively fast and allow goodthroughput for the semiconductor manufacturing process. Laser ashing mayalso limit polyimide undercutting and be highly selective to polyimide,so that the semiconductor chip is not damaged during polyimide removal.An ultraviolet (UV) laser is used to ash, or ablate, the polyimide, aspolyimide has a relatively high light absorption coefficient in the UVrange and a low threshold to initiate ablation. Laser ablation is aline-of-sight, anisotropic method, which significantly reduces the riskof polyimide undercutting. Laser ablation of polyimide may also be arelatively low temperature process, under 150° C. in some embodiments.The polyimide removal process may include relatively short plasmacleaning steps before and after laser ablation of the polyimide toremove any carbon debris or residue that may be on the semiconductorchip.

FIG. 1 illustrates a flow chart of an embodiment of a method 100 forlaser ashing of polyimide. FIG. 1 is discussed with reference to FIGS.2-7. A diced wafer 200 including a supporting material 203 attached to asemiconductor chip 202 by a polyimide glue layer 201, such as is shownin FIG. 2, is provided. Supporting material 203 may be glass in someembodiments. Semiconductor chip 202 may be any type of semiconductorchip, and may include a silicon substrate with various structures madefrom materials including but not limited to silicon oxide, siliconnitride, or metal. In block 101, as is shown in FIG. 3, the supportingmaterial 203 is released using a laser 301. Laser 301 causes thepolyimide glue layer 201 to release the supporting material 203. Thelaser release of supporting material 203 does not remove the polyimideglue layer 201 from semiconductor chip 202. The laser release ofsupporting material 203 may have a process time of about 10 minutes insome embodiments, and may be achieved using a laser 301 having a fluenceof about 110 millijoules per centimeter squared (mJ/cm²), a laserrepetition rate of about 100 Hertz (Hz), and a stage speed of about 5millimeters per second (mm/s) in some embodiments.

After laser release of supporting material 203 in block 101, a structure400 including the semiconductor chip 202 with polyimide glue layer 201remains, as is shown in FIG. 4. Then, in block 102, the polyimide gluelayer 201 and semiconductor chip 202 are cleaned using plasma. The firstplasma cleaning acts to clean any carbon debris that may be present onthe polyimide glue layer 201 after release of the supporting material203 in block 101, as the carbon debris may interfere with the laserashing process (discussed below with respect to block 103). The plasmacleaning step of block 102 may include placing the structure 400 in aplasma asher for a process time of less than about an hour, and may beperformed using 600 millitorr (mTorr) O₂ plasma at 1000 watts (W) insome embodiments. The relatively short process time for the plasmacleaning step of block 102 avoids damage to semiconductor chip 202.

Then, in block 103, a laser 501 is used to ash the polyimide glue layer201 as is shown in FIG. 5. The laser ashing, or ablation, acts to removepolyimide glue layer 201 from chip 202. Laser 501 is a UV laser, havinga wavelength from about 10 nanometers (nm) to about 400 nm. The fluenceof the laser 501 may be varied from about 100 mJ/cm² to about 300 mJ/cm²in various embodiments. The amount of polyimide removed per laser pulse(measured in nm per pulse) increases as the laser fluence is increased,for example, from about 27 nm/pulse at a fluence of 150 mJ/cm² to about63 nm/pulse at a fluence of 250 mJ/cm². In an exemplary embodiment,laser 501 may have a fluence of about 200 mJ/cm², a laser repetitionrate of about 200 Hz, and a stage speed of about 20 mm/s, resulting in aprocess time required for laser ablation of polyimide glue layer 201 ofabout 5 minutes. However, the laser repetition rate and stage speed oflaser 501 may also vary in various embodiments. As many as fifteen (15)passes across polyimide glue layer 201 by laser 501 may be required forfull ablation of polyimide glue layer 201 in some embodiments. Polyimidefumes may be generated during laser ablation of polyimide glue layer201, so a fume extraction device may be provided evacuate fumes anddebris from the laser ablation apparatus. A debris shield, which may bemade from a material that is transparent in the UV range such as fusedsilica, may also be used to protect the optics of laser 501. The debrisshield may be located between the source optics of laser 501 and thepolyimide glue layer 201.

After the laser ashing of polyimide glue layer 201 in block 103, astructure 600 including the semiconductor chip 202 remains, as shown inFIG. 6; however, structure 600 may include some carbon residue left overfrom the laser ashing process. Therefore, in block 104, a second plasmacleaning step performed to clean any remaining carbon residue that maybe present on the semiconductor chip 202. The second plasma cleaningstep of block 104 may include placing the structure 600 in a plasmaasher for a process time of less than about an hour, and may beperformed using 600 millitorr (mTorr) O₂ plasma at 1000 watts (W) insome embodiments. The relatively short process time for the plasmacleaning step of block 104 avoids damage to semiconductor chip 202.

Lastly, in block 105, a top chip 701 may be attached to thesemiconductor chip 202 by a connection layer 702 to form semiconductordevice 700. Top chip 701 may include any appropriate type of chip andmay be attached to semiconductor chip 202 in any appropriate manner. Inembodiments in which top chip 701 is connected using a flip chiptechnique, connection layer 702 may include a C4 layer, which maycomprise solder bumps, and may be deposited on receiving pads located onthe semiconductor chip 202. Top chip 701 and connection layer 702 areshown for illustrative purposes only; any appropriate devices may beconnected to semiconductor chip 202 to form a final semiconductordevice.

The technical effects and benefits of exemplary embodiments includeincreased throughput for a semiconductor manufacturing process whilereducing damage to a semiconductor chip during polyimide glue removal.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A system for laser ashing of polyimide for a semiconductormanufacturing process, the system comprising: a semiconductor chip; atop chip attached to the semiconductor chip by a connection layer; asupporting material; a polyimide glue layer disposed between thesupporting material and semiconductor chip; a plasma asher; and anashing laser configured to ash the polyimide glue on the semiconductorchip.
 2. The system of claim 1, wherein the ashing laser comprises anultraviolet (UV) laser.
 3. The system of claim 1, further comprising afume extraction device configured to remove polyimide fumes formedduring ashing of the polyimide glue from the system for laser ashing ofpolyimide.
 4. The system of claim 1, further comprising a debris shieldlocated between the ashing laser and the polyimide glue, the debrisshied comprising a material that is transparent in a wavelength of theashing laser.
 5. The system of claim 4, wherein the debris shieldcomprises fused silica.